Intermediate electrode in incandescent cathode tube



Jan 4 1927. 1 w. SCHOTTKY INTERMEDIATE ELECTRODE IN INCANDESCBNT CATHODE TUBE Filed August 30, 1921 QM Walt 3W Patented Jan. 4, 1927.

UNITED STATES PATENT OFFICE.

WALTER SCHOTTKY, OF WURZBURG, GERMANY, ASSIGNOR T SIEMENS & HALSKE AKTIENGESELLSCHAFT, OF SIEMENSSTADT, NEAR BERLIN, GERMANY, A COB- PORATION OF GERMANY.

INTERMEDIATE ELECTRODE IN INCANDESCENT GATHODE TUBE.

Application filed August 30, 1921, Serial No. 497,005, and in Germany January 23, 1917.

My inventionrelates to'intermediate elec-' trodes in incandescent cathode tubes.

It is a frequent practice to introduce intermediate electrodes with apertures into ina' candescent cathode tubes; these perforated electrodes either serve for controlling the design of such intermediate electrodes which during the operation, either-continuously or during a certain phase of the electric process,

possess a positive potential as against the incandescent cathode; as" compared with hitherto known forms ofconstruction, the present form offers very material advanta es. dhe efiiciency of an electric discharge tube being mainly determinedby the amount of 1 current emanating from the anode,'it is oh-s vious that the current intercepted by theintermediate electrode is lost in so far as the amplifying, rectifying orwavereducing,- action of an incandescent catho e tube is f concerned. For thisreason it is'necessary to construct the intermediate electrodes in 4 f such a way that they intercept only a very small portion ofthe electron current passing through. In cases where it.was impracticable' to keep the intermediate electrode concerned permanently at negative poten tial as against the cathode a solution of this 40 problem has hitherto been attempted byconstructing the body of such an intermediate electrode ofthin wires which are for instance Wound upon a. small glass frame.

However, this construction of electrodes '45 has a drawback which has hitherto escaped notice. For establishing a basis -for the following consideration it is intended first of all to contemplate a case in whichthe intermediate electrode has the efiect ,of a space charging screen, i. 'e. in which the perforated electrode interposed between the glow-cathode and auxiliary screen, by means of the positive potential impressed upon it, is to neutralize the space charging effect of the electrons, thus rendering the positive control of large quantities of electrons possible.

In this case a field exists between the cathode and space charging screen as also between the latter and the auxiliary screen, this field tending to draw the electrons towards the, space charging screen. Consequently, it is not suflicient to prevent the electrons which are to reach the anode, from impingingupon the screen body of the space char ing screen during their first passage. It Wlll be necessary, moreover, to guard against any violent deflection (straying) of the electrons during theirpassage through the screen because, according to the law of energy, any gain in lateral velocity dueto the deflection will be attended by a corresponding loss of velocity in the normal direction. This loss may easily increase to such an extent that the electron so aflected is seizcd by the field directed to the rearward this manner, the advantages which thin wires offer with respect to intercepting effeet, are partly neutralized again by their straying action. Even if care be taken by the overlapping anode field, that the majority of-the electrons deflected pass through the auxiliary screen, and overto the anode, the sharpness of the current rise with changing screen potentials is, nevertheless considerably impaired by this deflection, and it may happen that, more especially in amplifier tubes and in amplifier rectifier tubes, the

action of the space charging screen is ren ,dcred almost void.

Additional disadvantages of screen bodies of thin wires for the space charging screen.

are the following: Owing to the stray fields plane for neutralizing the space charging effect. This, however, entails a stron er stray effect and therefore, a stronger dis charge of the electrons into the space charging screen. Finally it may happen with arrangements consisting of very thin wires that owing to the deflected electrons which frequently hover around the wires of a space charging screen, local space charges are produced there which partly neutralize the effect of the positive charges accumulating there, thus resulting in the necessity of further increasing the potential at the screen body.

In cases where a fieldfor accelerating the electrons exists behind the intermediate electrode, the discharge of deflected electrons to the positively charged intermediate electrode does not matter. But even in this case the stray eflect on the screen wires is objection able inasmuch as in the auxiliary screen the sharpness of the directive force is impaired, Whereas in the anode protecting screen the electrostatic screening effect is reduced so that also in this case, the employment of bodies consisting of thin wires is a disadvantage. In wave generating tubes, moreover,

it may happen that the auxiliary electrode possesses a stronger positive potential as against the cathode than the electrode (anode) located hehind it. In such cases a strong stray action of the auxiliary electrode the electrode,

is equivalent to an actual loss of current for the anode, which 18 obvious from the expla- 'nation given above.

In such cases as described, according to the present invention the electrostatic advantages of solid electrodes are combined with the geometrical advantages of thin wire bodies by making the essential portions of the intermediate electrodes of very small sectional area in the direction of the plane of whereas in a direction at right angles thereto they are made of rather large size. Accordingly the essential parts of the electrodes may consist of strips of sheet metal placed on edge relatively to the electrode surface, these strips being arranged in grid fashion. If for instance the thickness of the sheet metal strips used is reduced to .1 to .2 millimetres, which otters no great difiiculties, the interceptingefi'ect of the electrodes is thereby reduced to a minimum whereas on the other hand a sufficient electrostatic eilect may be obtained by making the strips considerably wider (one half to several millimetres). A. particularly simple intermediate, electrode,

form of electrode of the type described is the following: A thin sheet is provided with parallel slits over the entire field in which it is to act as intermediate electrode. webs left standing between the slits are comparatively wide, e. g. 1 mm. By subse quently turning them through an angle of 90 degr. these webs are thus placed at right angles to the surface of the screen. If a cylindrical shape is selected for the electrode, which is particularly favourable for the space charging screen, it is natural that the direction of the slits must be parallel to the axis of the cylinder. In that case the turning of the webs at right angles to the surface of the screen would mean that they are all turned into radial alinement.

A perspective view of an incandescent cathode tube showing a space charging screen of the type described and an auxiliary screen of the same construction is illustrated in Fig. l of the accompanying drawin Fig. 2 represents a sectional View througi the entire arrangement of electrodes, whereas Figs. 3 and 4 are longitudinal sectional views of a cylindrical auxiliary screen and space charging screen alone.

The incandescent cathode consists of a wire kept under tension by a spring 7". It is surrounded by three concentric cylinders, the innermost of which represents the tension or space charging screen 7'; then follows the auxiliary screen it, and the outer cylinder is the anode a. Space charging screen 1' and auxiliary screen it consist each of one single piece of sheet metal into which parallel slits s have been punched. The comparatively wide webs If left standing between the slits s are placed at right angles to the surface of the sheet by subsequent setting, as may be seen from Figs. 2 to 4. Thereupon the perforated sheets are bent into a cylindrical shape in such a mannerthat the slits and webs run longitudinally in parallel to the axis of the cylinder, but the webs extend transversely in radial direction.

What I claim is:

1. In incandescent cathode tubes an anode, a cathode and at least one intermediate screen-like electrode, the essential parts of said screen-like electrode possessing a depth of material normal tothe surface of said intermediate electrode greater than the thick ness thereof, taken at right angles to said normal.-

2. In an incandescent cathode tube, an

The

anode, a cathode and at least one intermediate screen-like electrode, said intermediate electrode having webs between the screen openings, which consist. of sheet metal strips placed on edge against the surface of said so as to form a grid.

3. A grid electrode, comprising a plurality of thin strips of metal having a plurality of spaced thin metallic strips therebetween, 5. A grid electrode comprising a pair of said spaced strips being twisted. lateral members, and a plurality of cross L A grid electrode comprising a sheet of members integral therewith, the plane of 10 metal having a plurality of apertures out each cross member being twisted relative to therein, the strips of a metal between said the plane of said lateral members. apertures being twisted without changing In testimony whereof I afiix my signature. the general configuration of said sheet. WALTER SCHOTTKY. 

